The present invention refers to processes for the treatment of residual liquors, and more particularly to a process for the treatment of residual liquors from the ammoniation and carbonation of alkali metal salts for producing ammonium salts.
In agriculture, a great variety of substances are used as fertilizer. An example of the above referred substances is sodium nitrate, which has the characteristics of a good quality fertilizer and abounds in natural form in countries such as Chile. In fact the sodium nitrate was the first nitrogenous mineral fertilizer used by the human been.
The nitrogen contained in the Chilean nitrate can be totally assimilated by plants, but despite its abundance, it has two basic disadvantages:
The first disadvantage of the sodium nitrate is related to its high sodium content (36.4% expressed as Na2O) which significantly raises the salinity of the soil, and thus decreases the productivity of the farm.
The second disadvantage of the sodium nitrate is related to its low nutrient content, since it contains only 16.5% of nitrogen compared with the nitrogen content of a good quality nitrogenous fertilizer which is about 46.4%, or to the nitrogen content of the ammonium nitrate which is about 35.0%. When a fertilizer has a low nutrient contents a higher quantity of fertilizer is needed and therefore the fertilization costs by nutrient unit are higher than the fertilization costs when using a good quality fertilizer.
As it was previously described, the ammonium nitrate has a nutrient content of 35%, which makes this substance a very suitable fertilizer for commercial purposes.
With regard to the ammonium nitrate, there are actually many commercial processes for its production, which use as raw materials ammonium and nitric acid. The main differences between those processes are related to the design of the reaction equipment used, which has influence on the process performance. A good reaction equipment means an overall satisfactory performance and a good use of the energy generated by the reactions. Another difference between those processes is related to the appearance of the final product, which may be shaped like pearls or granules of different densities and porosities, or may be diluted in a solution together with other fertilizer compounds such as the Urea (UAN 32) in order to be irrigated.
When the sodium nitrate was partially displaced from the market by other nitrogenous fertilizers due to its low nutrient content and its high sodium content, there were developed alternative processes in order to eliminate its sodium content and raise its nutrient content. Thanks to these processes, it is avoided the waste of a natural resource having a high value.
In one of these processes, the sodium is substituted with potassium, which is the third element of the so-called xe2x80x9cmajor nutrientsxe2x80x9d for plants, being the nitrogen the first element and the phosphorus the second. Said process comprises mixing potassium chloride and sodium nitrate solutions on such proportions that a double crystallization is induced by partially evaporating the water contained in said solutions. The sodium chloride is crystallized before the potassium nitrate. By this process, there are eliminated ions which are harmful for the soil, such as chlorides and sodium.
In other known process, the sodium nitrate is reacted with sulfuric acid in order to be transformed on nitric acid which is then reacted with ammonium in order to produce ammonium nitrate and sodium sulfate which is separated by crystallization. This process is only suitable when there are plenty of cheap disposals of sodium nitrate and sulfuric acid available and when the cost of the sodium sulfate is very high.
In view of the abundance of the sodium nitrate and the benefits of the ammonium nitrate, applicants developed a process for the treatment of residual liquors from the ammoniation and carbonation of alkali metal salts -SOLVAY processxe2x80x94containing an ammonium salt mixed with a sodium salt, soluble sodium bicarbonate, and water, and producing ammonium salts.
Applicants process comprises the steps of: eliminating the sodium bicarbonate, and ammonium bicarbonate mixed in the residual liquor by mixing sulfuric acid with the residual liquor in order to obtain a solution of an ammonium salt and a sodium salt; and separating the sodium salt from the ammonium salt solution or mixing the solution of an ammonium salt and a sodium salt with sodium chloride crystals in order to obtain a magma containing sodium salt crystals and ammonium chloride crystals and separate the sodium salt crystals and the ammonium chloride crystals from the magma.
The sodium bicarbonate and the sodium carbonate may also be produced world-wide by a process called xe2x80x9cDual-salt Ammonium Chloride Processxe2x80x9d, which is in fact, a variant of the xe2x80x9cSOLVAYxe2x80x9d process, in which the ammonium, carbon dioxide, calcium carbonate and sodium chloride are used as raw materials, by which it is obtained a by-product comprising a solution of ammonium chloride.
Applicant process in comparison with the SOLVAY process, uses as sodium source, a sodium salt such as sodium nitrate by which it is produced ammonium nitrate which is a fertilizer having a higher nitrogen content than the ammonium chloride (35.0% of nitrogen content versus a 26.0% respectively). Among other differences between the SOLVAY process and applicants process are:
By the use of a sodium salt instead of sodium chloride there are obtained solutions with higher concentration of ammonium nitrate or ammonium chloride respectively, thus reducing evaporation costs. Furthermore, if the ammonium nitrate is enriched with urea it may be commercialized as a nitrogenous solution.
In applicant""s process, thanks to the addition of sulfuric acid to the waters generated by the filtration of the sodium bicarbonate, it is totally used the sodium contained in the sodium nitrate, transforming the nitrates on ammonium nitrate, and additionally producing sodium sulfate.
The ammonium nitrate has many advantages compared with the ammonium chloride when there are used as fertilizer, thanks to the fact that the 50% of its nitrogen content remains in nitric form, which is immediately available for the plants when it is applied to the soil, which it is not possible when used in ammonium form because it has to be converted to a nitric form.
The transformation of nitrogen ammoniacal forms on nitric forms, is a natural phenomenon, which occurs in the soil by the enzymatic and bacteriologic reaction of the substrates contained in the soil. Therefore, if the bacteriologic activity of the ground is slow, xe2x80x94which occurs in cold climatesxe2x80x94the ammoniacal nitrogen can not be properly used by the plants since a low rate of transformation of ammoniacal forms to nitric forms generates nitrogen loses due to de-nitrification, leaching and hydrolysis phenomena and to the evaporation of the ammonium before the plant is able to assimilate the ammoniacal nitrogen.
The ammonium chloride has a lower demand as a fertilizer compared to other fertilizers, mainly because certain cultivates such as tobacco, vegetables and some fruit trees are sensitive to the chloride ion.
Furthermore, the process of the present invention has some advantages compared with processes for the production of ammonium nitrate which use nitric acid as raw material:
The process of the present invention uses less energy that the ammoniac catalytic combustion processes.
The above referred processes consume an important volume of water in order to cool the absorption tower into which is transformed the nitrous oxides on nitric oxides which then have to be reacted with water in order to produce nitric acid, because during the ammoniac catalytic combustion processes a temperature of approximately 900xc2x0 C. is generated.
The plant in which are carried out the ammoniac combustion processes has to be equipped with expensive and sophisticated anti-pollution equipment in order to avoid nitrous gas emissions to the atmosphere. In comparison, with applicants process by the use of sodium nitrate for the production of ammonium nitrate it is avoided the emission of polluting residues.
It is therefore a main objective of the present invention, to provide a process for the treatment of residual liquors from the ammoniation and carbonation of alkali metal salts which produces solutions with a high concentration of ammonium salts, thus reducing evaporation costs.
It is also a main objective of the present invention, to provide a process of the above disclosed nature in which by the addition of sulfuric acid to the waters generated by the filtration of the sodium bicarbonate, it is totally used the sodium contained in the sodium nitrate, transforming the nitrates on ammonium nitrate, and additionally producing sodium sulfate.
It is an additional objective of the present invention to provide a process of the above disclosed nature which uses less energy than the ammoniac catalytic combustion processes.
It is another main objective of the present invention, to provide a process of the above disclosed nature in which the use of sodium nitrate for the production of ammonium salts does not generate polluting residues.
It is still another objective of the present invention, to provide a process of the above disclosed nature which does not consume great volumes of water.
These and other objectives and advantages of the present invention will be apparent to those persons having ordinary skill in the art, from the following detailed description of the invention.